In the manufacture of printed substrates, projection optical systems and projection exposure devices have been known for projecting images of original patterns on workpieces. In particular, Japanese Patent No. 3026648 discloses a unity magnification projection lens system that is symmetric about the center line of the lens system where a diaphragm may be placed, and the light beams entering and exiting the lens systems are at least nearly telecentric on both the object and image sides. Unity magnification imaging is based on the symmetry of the lens system about the center line where a diaphragm may be placed. However, generally creating a lens system that is perfectly symmetrical is very difficult due to manufacturing tolerances of the components, tolerances in assembling the components, and other factors. As a result, the imaging magnification tends to vary slightly from unity magnification. Therefore, each lens system must be individually adjusted during assembly.
Additionally, when exposing a plurality of patterns onto the same substrate, it becomes necessary to overlap and match the image accurately, generally requiring slight adjustments to magnification, corresponding to the expansion and contraction of a substrate with temperature changes and the like, prior to the exposures. Generally, in order to change the image magnification of a lens system, the entire lens system may be moved in the optical axis direction. However, with projection lens systems as described above, for which both the object side and the image side are made to be telecentric, magnification cannot be changed by moving the entire lens system in the optical axis direction while maintaining the telecentric conditions.
Furthermore, there is a demand for improvements of the known projection exposure devices of the type described above for exposing a larger area of a workpiece in a single projection exposure.
The present invention relates to a projection optical system and a projection exposure device, and especially relates to projection optical systems and projection exposure devices used in the manufacture of printed substrates and similar substrates. The projection optical system of the present invention is symmetrical about a center line where a diaphragm or stop is placed and remains at least very nearly telecentric on both the object and image sides as the imaging magnification is slightly varied to adjust for, for example, expansion and contraction of the substrate that accompany temperature changes, as well as to correct for variations from unity magnification due to manufacturing tolerances, while maintaining favorable correction of aberrations in all adjusted positions.